Ionizing radiation in the form of x-rays, gamma rays, high energy electrons etc. is extensively found in the medical and nuclear fields, and are often found in various industrial fields. For example gamma rays from Co.sup.60 radio therapy machines are utilized to expose medical patients during radiation treatment. Medical instruments are irradiated for sterilization, and certain plastics are irradiated to polymerize them. Workers involved in the generation of electricity in nuclear reactors or involved in the transfer of radio isotopes from a manufacturer to a customer are often exposed to radiation. In outer space, astronauts, electronic and other equipment are exposed to radiation.
It is clearly desirable to be able to measure the amount of radiation to which personnel, materials or structures are exposed. It is also highly desirable to be able to measure the radiation rate, i.e., the intensity of radiation, in addition to the total radiation dosage incurred.
There are presently three radiation dose monitoring techniques in general use: (a) thermoluminescent devices, (b) air ionization chambers, and (c) geiger counters. Both air ionization chambers and geiger counters measure dose rates (in some cases having an alarm threshold), but are large and bulky and require a high voltage supply, thus making them undesirable and impractical for use as direct reading dosimeters. In addition, their detection ranges are far above ranges useful for personnel, and insufficiently accurate for the same application. Consequently personnel dose measurement has fallen to thermal luminescent devices. Such devices utilize a small crystal of LiF or CaF.sub.2 which traps the electrons and holes produced by the ionizing radiation. When heated, light is emitted from the crystal due to the emptying of the traps and this light is related to the accumulated dose. Such devices give post-facto radiation measurements, and do not provide a warning threshold indication. Indeed, a person may exceed a safe dose substantially by the time his dosimeter is measured. Further, the dose rate at any given time cannot be indicated.
The present invention is a direct reading dosimeter which is light, sufficiently small to be able to worn on a person, and measures both dose rates and total dose. A dose rate or total dose threshold can be set whereby an alarm is sounded when any of the selected threshold is exceeded. Since either the dose rate or the total dose can be read out directly and immediately by the user, sudden increases or excessive radiation can be immediately responded to, the wearer retreating to a safe physical location. The measurement range has been found to include the range of most interest to personnel which might be exposed to radiation, such as workers in the medical, nuclear and industrial fields. Such irradiation is typically in the range of 0.01 to 10 cumulative rads.